Potentiometer



June'lz, 1928. 1,672,916

. 'J. C. SNELL PoTENTioMETER Filed Feb. 4, 1924 imm? J7.' Q fm11111@1111111111 Patented June l2, 1928.

JAMES C.

/PATENT oFFl-cE.

SNELL, OAK PABX, ILLINOIS, AS-SIGNOB .TO PREMIER ELECTRIC COM- PANY, OF CHICAGO, ILLINOIS, A. COBPORATION OF ILLINOIS.

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ppucauo'n sled February '4, 1924. serial No. 690,389.

The invention relates to potentiometers and more particularly to those adapted to be used for radio service.

The object ofthe invention is to provide a potentiometer with means whereby the circuit between the A and B batteries may be broken, thus breaking the plate voltage an'd insuring the filaments of the tubes against accidental rupture. Another object of the invention is to provide a potentiometer with an automatic cut-out or disconnector whichwill break the shunt circuit between the positive and negative terminals of the A battery caused when the main circuit between the A and B7 batteries is broken,

therebyf preventing a drain on, the A battery. Still another object of the invention is to provide improvised means for holding a switch arm against a resistance coll 1n which provision is made for removing the switch arm when desired.

The invention consists 1n the several novel features hereinafter set forth and more par-` ticularly defined by hereof.

In'the drawings: Fig. 1 is a rear View of a potentiometer embodying the invention. Fig. 2 is a front view. Fig. 3 is a section on line 3-3 of Fig. 2. Figs. 4 and 5 are detail views of the automatic cut-out or disconnecclaims at the conclusion tor. Fig. 6 is a diagrammatic view of the improved potentiometer applied to the plate circuit of a radio receiving system.

The invention is exemplified in a potentioxneter for the plate circuit oi' a radio receiving system which comprises an A battery l 7 connected by conductors 8 and 9 to the ilament of an `electron tube 10, a pair. of phones 12 connected by conductor 11 to the plate of the tube, a B battery 13 connected Vto the phones 12 by a conductor 14 and a potentiometer 15 disposed between the A and B batteries, toregulate C.the voltage and the amount of plate` current v7passing through the conductor 8 and the tube 10.

The potentiometer comprises a circular insulated base 20, a sleeve 22 extending through the center of the base 20, and a dial 23 secured on the sleeve by a nut 27, and adapted 5U to be positioned against the panel of the -usualradio apparatus container. A shaft 28 with an integral switch arm 29 at one end thereof extends through the sleeve 22, and at the opposite end adjacent the dial a pointer 30'and a handle 31 are securedto the shaft by a screw 32.

An insulated coro 34 is disposed in a cir- Y cular slot 33 in the base 20. A resistance coil 35 of suit-able ribbon or wire is wound around core 34 and is adapted to be engaged by the switch arm 29 as it rotates with the shaft 28, when manually operated to control the direction and the amount of current passing through the resistance coil. One end of wire-coil 35 is connected by a screw 37 to a terminal plate 36 which is secured by a screw 39 to the insulated base 20 and is adapted to receive conductor 16 from the negative terminal of the A battery 7. The other end of the resistance coil 35is connected by an insulated wire conductor 41 which is disposed in a slot 43 in base 20, to one end of a spring conductor 42 which is secured to the base of a screw. The spring conductor has a raised ortion, adjacent one end of coil 35 whichv 1s adapted to engage the switch arm 29. as it passes over spring conductors 42. A at late 45 of conductive material is secured to t e bottom of spring conductor 42 and normally engages a contact stud 46 on terminal 47 which is secured to base 20 by a screw .48.

On the bottom of switch arm 29 an insulated strip 49 is secured .so that when the switch arm is rotated and passes oit the resistance coil 35, it will engage the raised portion of the spring conductor 42 and force it inwardly thereby causing the plate 45 to leave the contact stud 46 and break the circuit between terminals 36 and 47.

By allowing a space on the insulated core 34 to be left atI the end of the resistance coil 35, means is provided for breaking the plate circuit between the A and B batteries.

A terminal 50, adapted to receive the conductor from the B battery is disposed between the terminals 36 and 47 on the base 20 and is secured thereto by a screw 58. The upper end of terminal 50 has a hole through which the shaft 28 passes.` A plate 52 is rigidly secured by a stud 53 to the terminal 50 and has a hole adjacent the hole in the terminal 50 which acts asa seat for the inner end of the switch arm 29. Adjacent plate 52, a plate 55 ispivotally secured thereto by a stud 54 and is adapted to engage the outer end of switch arm 29 so as to hold shaft 28 from lateral displacement; This exemplies means for holding switch 29 in pressed relation against the resistance coil 35. By swinging plate 55 awa from the switch arm 29 and b loosening t ie set screw 32, the shaft 28 an switch arm 29 may be removed.

The operation of the potentiometer will be as follows. The current from the B battery will enter the potentiometer at terminal and will be conducted through the switch arm 29 to the resistance coil 35. At this point the current will branch in two directions, art of the current flowing through the resistance coil at'one side of the switch arm and out by `way of the terminal 39, the other portion of the current flowing through the remainder of the resistance coil 35, conductr 41, flat spring conductor 42, and terminal 47. When the circuit between the A and B batteries is to be broken, the switch' arm 29 will be rotated until it leaves theresistance coil 35, as at 60, 'As it leaves the `coilthe underside of the switch arm 29will engage the raised portion 36i of the spring conductor 42, and cause it to be forced inwardly, thereby' disconnecting the plate 45 and ystud 49 and breaking the shunt circuit across the positive and negative terminals of the A battery. e

The invention-exemplifies an improved p0- tentiometer'in which provision is made for disconnecting the circuit between the A and B batteries thereby insuring the tubes against accidental rupture, and in which provision is made for simultaneously breakving the shunt circuit between the positive and negative terminals of the A battery when the circuit between the A and B batteries is broken, thereby eliminating the drain on the A battery. y

The invention is not to be understood as restricted to the details set forth,'since these vmay be modied within the scope of the appended claims, without departing Jfrom the spirit and scope of the invention. e

Having thus described the invention, what I claim as new and desire-to secure by Letters Patent, is: i

1. The combination with a source of electrical current, a circuit for said source of current, and a lsecond source of electrical current, of a potentiometer comprising a resistance element connected in shunt with said circuit, a `contact connected to said second source of current, saidcontact being movable 'over said resistance element to include more or`less of and movable o said element, and means controlled bythe con'- tact in its off position to break thecircuit` through the resistance element and prevent the flow of current from the first mentioned source of current through said resistance element. y

2. The combination with a source of elec- .trical current, a circuit for said source of 3. The combination with a plate circuit oi a radio -receiving system comprising an A battery, a circuit for said battery, and a B battery, of a potentiometer comprising a resistance element connected in shunt with said circuit,- a contact connected, tol said B battery, said contact being movable over said resistance element to include more or less of and movable oli' said element, and means controlled by the contact in its oli position to open the circuit through the resistance elementand prevent the flow of current from the A battery through said resistance element.v

4. In an electrical controlling device, the combination of a supporting member a resistance element mounted on said meiber, a

contact member having its inner end slid.

ably and pivotally mounted in said supporting member and its outer end movable over the resistance element to include more or less thereof, and an arm having its inner end adapted vto bear against the contact member' to press it against the coil and its outer end pivoted to the base to permit the arm to be rotated out of engagement with said contact member so that. the latter may be removed romthe base. s

5. In a potentiometer, a resistance winding, a terminal plate having a permanent electrical connection toone end of said winding, a second terminal plate with a spring connection to the other end of said winding, a switch arm normally in contact with Said winding, a third terminal connected `electri' cally to said switch arm means for o 'erating the switch arm to disengage sai arm from said winding, and lmeans operating as. an incident to the disengagement of said arm, for breaking the spring connection betweensaid second Iterminal plate and said v ing, a terminaLplate having'a permanent electrical connection to one end ofsaid winding, a second terminal plate with a spring 'forbreaking the spring connection between connection to the other end of said winding,s said second terminal plate and the resistance a switch arm normally in contact with said winding, when said arm is disengaged from 10 winding, a third terminal connected electrisaid winding.

ing a switch arm to disengage said arm from of December 1923.

cally to said switch arm, means for operat- Signed at Chicago, Illinois this 18th day said winding, and a projection on said arm JAMES'. C. SNELL. 

